1. Technical Field
The present invention relates to safety devices and a method of manufacture thereof and, more particularly, to medical devices including hypodermic needles having a safety device provided therewith and methods of manufacturing the same.
2. Background of Related Art
There is a known problem associated with hypodermic needles, which is that once a hypodermic needle has been used on a patient, it may be contaminated with an infection from the patient, and there is therefore a risk that the needle may pass on the infection if it is allowed to come into contact with another person. Similarly, if a needle accidentally pricks one person before it is used on a patient, an infection may be passed onto the patient from the person accidentally pricked. Undesirable pricking of this nature will hereinafter be referred to as “needle stick”.
A number of safety devices have been proposed in an attempt to counter the above described problems. Some such devices are combined needle and syringe arrangements in which the needle may be retracted into the body of the syringe by applying additional pressure on the syringe plunger once it has been pushed to the end of the syringe cylinder (i.e. once all of the fluid to be injected has been ejected from the syringe). While the syringe and needle arrangement is transported and stored, a plastic cap is fitted over the needle. There are a number of problems with a device of this type. Firstly, this device is only suitable for injecting fluid into a patient and not for taking a sample from a patient because the retraction of the needle is activated once the plunger is fully pushed into the cylinder and not when it is partially withdrawn from the cylinder as would be the case after the taking of a sample. Also, the person who is to give the injection must remove the plastic cap some time before the injection takes place, and from this moment on until the needle is retracted, the device is unsafe. Once the injection is completed, the operator of the needle must remember to perform the action to cause the needle to retract. To maximize safety, this should be performed whilst the needle is still within the patient. However, this is painful for the patient. Also, the operator may simply omit to retract the needle for whatever reason, thus leaving the needle exposed and unsafe.
To counter this last problem, it has been proposed to include a time fuse mechanism which is activated upon, for example, hydration (e.g. by receiving a blood sample or a liquid to be injected into the syringe). However, the needle will be unsafe for the duration of the time fuse period and can cause problems if, for example, the retraction is automatically activated during an injection.
U.S. Pat. No. 5,976,111 describes an alternative safety device for a hypodermic needle. The described device includes a stem portion through which fluid may flow between the syringe mounted on a proximal end of the stem and a needle mounted on a distal end of the stem. Telescopically mounted around the stem is a sheath cylinder. The sheath cylinder may slide over the stem from a first, exposed, position in which the point of the needle is exposed, to a second position in which the whole of the needle is covered by the sheath. A helical metal spring urges the sheath into the second position. A pair of leaf spring arms which are biased radially outwardly are mounted onto the stem and lock the sheath in the second position (the needle is therefore safe while the sheath is locked in the second position). A ring is also slidably mounted on the stem and may be used to unlock the sheath by forcing the leaf spring arms flat into the stem portion to permit an injection to take place. During an injection the skin of the patient pushes the sheath cylinder (and also the unlocking ring) back into the first position, exposing the needle point which may therefore pierce the patient's skin. Upon completion of the injection, the sheath is urged back (due to the spring) into the second position as the needle is withdrawn from the patient, thus re-covering the needle. While the sheath is pushed back over the stem portion towards the first position, the unlocking ring is also pushed back into a position where it no longer restrains the leaf spring arms; therefore, when the sheath cylinder returns back to the second “safe” position the leaf spring arms are released and they spring out into locking engagement with the sheath to prevent the sheath from sliding back into the first, exposed, position again.
The device described in U.S. Pat. No. 5,976,111 satisfies many of the safety requirements associated with hypodermic needles discussed above. However, it nonetheless suffers from a number of problems, which it would be desirable to overcome. All of the described embodiments of the device require at least five separate components to be manufactured and then assembled. This renders the cost of the device significantly more than a conventional needle and needle-luer combination (a needle-luer is a small member which is adapted to fit onto a syringe and into which the base of the needle is mounted). Also, because the needle is mounted directly to the stem of the described safety device, a needle manufacturer would have to significantly alter its conventional manufacturing process for producing needle and needle-luer combinations to manufacture the described device.
The present invention seeks to provide an alternative safety device for a hypodermic needles and the like.